Instrumentation and techniques of high resolution mass spectrometry are being developed and employed for studying problems of structure, biosynthesis, and drug metabolism, with special attention directed toward antibiotics (especially pactamycin, peptide, polyene and ansamycin antibiotics), biologically active marine natural products, and nucleosides. These techniques include field desorption mass spectrometry (at high and low resolution), especially at high masses, and gas chromatography-mass spectrometry (at high and low resolution); utilizing electron impact, field ionization and chemical ionization; employing capillary as well as conventional columns.